The invention relates to a method and an apparatus for overload-free driving of an actuator, for example of an electric motor for the folding function of exterior mirrors of a motor vehicle.
In the context of driving actuators, the problem of protecting the actuator against overload often arises. This is because actuators, for cost reasons, are usually not designed for continuous operation. If the actuator is driven so often that the actual average power produced by the actuator is greater than the rated power of the actuator for a relatively long time (for continuous operation), then there exists the risk that the actuator may be destroyed. The risk of destruction is thereby higher, the greater the extent to which the actuator was underdimensioned.
For overload-free driving of an actuator, it has become known in the prior art, for example from U.S. Pat. No. 4,721,894 (German patent DE 38 18 722 C2), to monitor the temperature or the power actually produced by the actuator and to switch the actuator off as soon as the permissible power or permissible maximum temperature of the actuator is exceeded. However, this requires power sensing or temperature sensors. Therefore, the realization of corresponding apparatuses for overload-free driving of an actuator is often too costly.
Furthermore, it is known to dispense with sensors for power or temperature monitoring of an actuator and merely to count the number of activations, calculated from a first activation, and to necessarily comply with a predetermined pause time after a predetermined maximum number of activations has been reached. This method has the disadvantage that the actuator must be dimensioned with such a (high) power that the maximum possible number of activations can be carried out even when no pause at all is complied with between the individual activations. The pause time likewise has to be fixed at a sufficiently large value for this worst case scenario. The pause time is complied with irrespective of the pauses with which the actuator is driven.
Furthermore, it is known for the actuator to be deactivated after a fixedly predetermined times calculated from a first activation, for a specific fixed pause time. However, in this case, too, the actuator has to be dimensioned such that it can be activated continually, i.e. without an interim pause, within the fixedly predetermined time. The pause time is complied with even when the actuator has only been driven a single time.
It is accordingly an object of the invention to provide a method and an apparatus for driving an actuator, which overcome the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which can be implemented in a simple and cost-effective manner, in particular without additional sensors for the actuator and in which unnecessary deactivation of the actuator for an unnecessary length of time is avoided as far as possible.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of driving an actuator and protecting the actuator against overload, which comprises the following method steps:
generating a drive signal for the actuator until the actuator has completely performed a requested function;
incrementing an activation counter each time an activation request signal is received;
generating a drive signal for the actuator upon receiving an activation request signal only if a counter reading of the
activation counter is no more than (less than, or less than or equal to) a predetermined maximum counter reading;
decrementing the counter reading in each case if a time since a last generation of the drive signal or since a deactivation of the drive signal is no less than (greater than, or greater than or equal to) a given interval time, or if a time since a last decrementing of the activation counter is no less than (greater than, or greater than or equal to) the interval time.
In accordance with an alternative embodiment of the invention, the method comprises:
decrementing an activation counter each time an activation request signal is received;
generating a drive signal for the actuator upon receiving an activation request signal only if a counter reading of the activation counter is no less than a predetermined minimum counter reading;
incrementing the counter reading in each case if a time since a last generation of the drive signal or since a deactivation of the drive signal is no less than a given interval time, or if a time since a last incrementing of the activation counter is no less than the interval time.
In other words, each time an activation request signal occurs, a drive signal for the actuator is generated only when the counter reading of the activation counter is less than a predetermined maximum counter reading (or is less than or equal to a predetermined maximum counter reading).
Accordingly, the actuator must be dimensioned such that it can be activated successively, without an interim pause, as often as corresponds to the maximum possible counter reading.
The counter reading is in each case decremented if the time since the last generation (or ending) of a drive signal (which leads to incrementing of the activation counter) is greater than (or greater than or equal to) a predetermined or predeterminable interval time or if the time since the last decrementing of the activation counter is greater than (or greater than or equal to) the interval time. In this case, the interval time should be chosen at least to be greater than the maximum possible activation time of the actuator if the interval time is calculated essentially from the beginning of the activation request signal or the drive signal. Otherwise, this condition is obviated.
In many applications it will be possible to assume that the activation time of the actuator lies at least within a relatively narrow, predetermined temporal range. By way of example, the folding in of an exterior mirror and folding out of an exterior mirror will essentially always require the same amount of time. It is therefore possible, without significant disadvantage, for the interval time to begin with the activation request signal or the drive signal.
What is achieved with the method according to the invention is that, in the event of a plurality of successive activations of the actuator, at time intervals shorter than the predetermined interval time, the activation counter is incremented without any decrementing up to the maximum value and, after the maximum value has been reached, further drive signals for the actuator on account of further activation request signals are suppressed. If activation request signals arrive at time intervals longer than the interval time, then the activation counter is decremented once or a number of times (at most down to the value zero).
This method therefore reacts very flexibly to the frequency of occurrence of activation request signals and the time intervals thereof. Unnecessary pause times do not occur. The actuator is nevertheless reliably protected against overloading.
According to one refinement of the invention, the generation of a drive signal for the actuator can be suppressed, after the maximum counter reading has been reached, for a fixedly predetermined or predeterminable pause time.
In accordance with an added feature of the invention, the generation of a drive signal for the actuator, after the maximum counter reading has been reached, is prevented until the counter reading of the activation counter is less than or equal to a predetermined or predeterminable value. By way of example, the generation of a drive signal can be permitted again only if the value of the activation counter had been decremented down to zero.
According to one refinement of the invention, the interval time is chosen such that the average power of the actuator, in the event of periodic driving with a period corresponding to the interval time [(interval time calculated from the beginning of the drive signal) or, in the event of periodic driving with a period corresponding to the maximum duration of the drive signal plus the interval time (interval time calculated from the end of the drive signal)] essentially corresponds to the maximum permissible average power. This is necessary in order to prevent overloading of the actuator in that steady state in which the activation counter is in each case incremented by an activation request signal (and generation of a drive signal for the actuator) and, immediately after the interval time has elapsed and a corresponding decrementing of the activation counter, an activation request signal arrives again.
The apparatus according to the invention comprises a counter unit, which forms the activation counter, and a counter/timer unit, which generates a signal for decrementing the counter unit at essentially periodic intervals.
The counter/timer unit may have a resettable or programmable counter, the counter reading being set to a predetermined or predeterminable counter reading each time an activation request signal occurs. The effect achieved in this way is that the interval time in each case begins with the arrival of an activation request signal for the actuator.
This is not absolutely necessary, however. Rather, the counter/timer unit can also generate the decrementing signals nonsynchronously with the activation request signals. In this case, however, it is necessary to suppress a signal for decrementing the activation counter during the actual activation time of the actuator.
As already explained above, it is possible to place the starting point of the interval time both at the beginning and at the end of a drive signal for the actuator. If the pause between two successive activation request signals amounts to a multiple of the interval time, then the beginning of a new interval time is defined by each end of the preceding interval time. In this case, the activation counter is decremented with each end of an interval time.
The method according to the invention can be realized in a simple manner by means of a customary microprocessor circuit or a microcontroller in conjunction with a program which processes the method.
An apparatus according to the invention can have the required activation counter unit and a counter/timer unit as hardware. However, these units can likewise be realized as software in conjunction with customary microprocessor circuits or microcontrollers.
Instead of the activation counter being incremented when an activation request signal occurs, and the counter being decremented in longer pauses, it goes without saying that it is also possible for the activation counter to be decremented by activation request signals. In this case, the counter is correspondingly incremented in longer pauses.
With the above and other objects in view there is also provided, in accordance with the invention, in combination with an apparatus for driving an actuator having an input receiving an activation request signal and a drive output for driving the actuator, a computer program product comprising a computer-readable medium having stored thereon program code for executing the above-outlined methods.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and apparatus for overload-free driving of an actuator, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.